This means Disney's strategy is working in regards to princess movies, and it's not surprising. As with Tangled, they used a gender neutral anme and focused at least half the marketing on the non-princess characters. It helps get boys interested in a movie that they would probably like regardless but might not have given a chance.
Frozen in particular works because Elsa has super-powers, and to boys she may as well be a superhero. They also might have a little crush on her, as I can recall when I was young my first crushes were in fact cartoon characters. Whatever the cause, Frozen seems to have crossed gender boundries, which is a great thing for Disney.